DRV8329: BEMF sensing resistor divider tolerance requirements

Om Dave

Prodigy 50 points

Part Number: DRV8329

Tool/software:

Hi Expert,

Have a nice day!

I have one question about DRV8329-Q1.

Customer wants to use FOC by DRV8329-Q1 and we are facing efficiency issues wrt current draw and the current ripple of the supply when compared to a competitor controller board.

Can you please provide the accuracy requirements for phase voltage measuring resistors? And can it be one of the factors affecting the efficiency?

We have changed the current shunt resistor from tolerance 1% to 0.1% as mentioned in one of the posts on this forum.

The operation conditions:

Operating voltage range: 16 V - 32 V

Maximum current draw : 15 A

Speed accuracy requirement: 1%

Reference :

6 months ago

0 Yara Al Shami 6 months ago

TI__Genius 14835 points

Hello!

Is this your own design or are you using the EVM?

I'm not sure entirely what could be causing the current draw and ripple but have you tried testing with different resistor values for the voltage divider?

There are also some good references for FOC using 1-shunt resistor:

https://e2e.ti.com/support/motor-drivers-group/motor-drivers/f/motor-drivers-forum/1041426/foc-field-oriented-control-with-1-2-or-3-shunt-configurations

https://www.ti.com/lit/ug/tiducy7/tiducy7.pdf

Regards,

Yara

0 Om Dave 6 months ago in reply to Yara Al Shami

Prodigy 50 points

Hello ,

This is our own custom design , that is why I wanted to understand what are the tolerances that are used in the EVM to get that possible point of failure out of the way.

We haven't tested it using a different divider for voltage sensing, we have used 100k and 4.7k as the divider as opposed to 100k and 4.9k in the EVM but have made the relevant changes in the VOLTAGE_BASE macro in the code

Thank you for the resources regarding the shunt resistor.

0 Yara Al Shami 6 months ago in reply to Om Dave

TI__Genius 14835 points

Hi Om,

The tolerance on the resistor used on the EVM is 1%

Om Dave said:
but have made the relevant changes in the VOLTAGE_BASE macro in the code

Has this affected the efficiency at all?

Regards,

Yara

0 Om Dave 6 months ago in reply to Yara Al Shami

Prodigy 50 points

Hi Yara,

We also have used 1% tolerance itself so it should not be a possible cause for concern then .

Yara Al Shami said:
Has this affected the efficiency at all?

We haven't tried changing it , we have put the calculated value as mentioned in the FOC Sensorless tuning guide.

Is there any resistor divided range where we can expect maximum efficiency ?

Or does changing the VOLTAGE_BASE without changing the divider resistors also can improve the efficiency?

Regards,

Om Dave

0 Yara Al Shami 5 months ago in reply to Om Dave

TI__Genius 14835 points

Hi Om Dave,

I don't have much knowledge on using our EVM with FOC but I think changing the resistor tolerance could help in getting a more accurate voltage reading. The EVM was designed to support trap commutation so I don't think it was optimally designed for FOC.

I think it would be difficult for me to determine what would increase the efficiency in your system, but increasing the voltage reading accuracy is on the right track.

Regards,

Yara

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DRV8329: BEMF sensing resistor divider tolerance requirements